Interconnect structures containing nitrided metallic residues

ABSTRACT

A metal cap is formed on an exposed upper surface of a conductive structure that is embedded within an interconnect dielectric material. During the formation of the metal cap, metallic residues simultaneously form on an exposed upper surface of the interconnect dielectric material. A thermal nitridization process or plasma nitridation process is then performed which partially or completely converts the metallic residues into nitrided metallic residues. During the nitridization process, a surface region of the interconnect dielectric material and a surface region of the metal cap also become nitrided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/891,869, filed May 10, 2013 the entire content and disclosure ofwhich is incorporated herein by reference.

BACKGROUND

The present application relates to a semiconductor structure and amethod of forming the same. More particularly, the present applicationrelates to an interconnect structure having improved reliability and amethod of forming the same.

Generally, semiconductor devices include a plurality of circuits thatform an integrated circuit (IC) fabricated on a semiconductor substrate.A complex network of signal paths will normally be routed to connect thecircuit elements distributed on the surface of the substrate. Efficientrouting of these signals across the device requires formation ofmultilevel or multilayered schemes, such as, for example, single or dualdamascene wiring structures. The wiring structure, which may also bereferred to as an interconnect structure, typically includes copper, Cu,since Cu based interconnects provide higher speed signal transmissionbetween large numbers of transistors on a complex semiconductor chip ascompared with aluminum, Al, based interconnects.

Within a typical interconnect structure, metal vias run perpendicular tothe semiconductor substrate and metal lines run parallel to thesemiconductor substrate. Further enhancement of the signal speed andreduction of signals in adjacent metal lines (known as “crosstalk”) areachieved in today's IC product chips by embedding the metal lines andmetal vias (e.g., conductive features) in a dielectric material having adielectric constant of less than 4.0.

In interconnect structures, electromigration (EM) has been identified asone metal failure mechanism. Electromigration is the transport ofmaterial caused by the gradual movement of the ions in a conductor dueto the momentum transfer between conducting electrons and diffusingmetal atoms. The effect is important in applications where high directcurrent densities are used, such as in microelectronics and relatedstructures. As the structure size decreases, the practical significanceof EM increases.

EM is one of the worst reliability concerns for very large scaleintegrated (VLSI) circuits and manufacturing since the 1960's. Theproblem not only needs to be overcome during the process developmentperiod in order to qualify the process, but it also persists through thelifetime of the chip. Voids are created inside the metal conductors ofan interconnect structure due to metal ion movement caused by the highdensity of current flow.

Although the fast diffusion path in metal interconnects varies dependingon the overall integration scheme and materials used for chipfabrication, it has been observed that metal atoms, such as Cu atoms,transported along the metal/post planarized dielectric cap interfaceplay an important role on the EM lifetime projection. The EM initialvoids first nucleate at the metal/dielectric cap interface and then growin the direction to the bottom of the interconnect, which eventuallyresults in a circuit dead opening.

SUMMARY

A metal cap, which is used to reduce electromigration, is formed on anexposed upper surface of a conductive structure that is embedded withinan interconnect dielectric material. During the formation of the metalcap, metallic residues simultaneously form on an exposed upper surfaceof the interconnect dielectric material. A thermal nitridization processor plasma nitridation process is then performed which partially orcompletely converts the metallic residues into nitrided metallicresidues. During the nitridization process, a surface region of theinterconnect dielectric material and a surface region of the metal capalso become nitrided. As a result of performing one of the nitridationprocesses, the resultant interconnect structure has lower currentleakage between adjacent metal lines and enhanced reliability ascompared to an equivalent interconnect structure in which nitridation isnot performed.

In one aspect of the present application, a method of forming aninterconnect structure is provided. In accordance with this aspect ofthe present application, the method includes providing at least oneconductive structure embedded within an interconnect dielectricmaterial, wherein the at least one conductive structure has an uppersurface that is coplanar with an upper surface of the interconnectdielectric material. A metal cap is then formed on the exposed uppersurface of the at least one conductive structure, and during theformation of the metal cap, metallic residues are simultaneously formedon the upper surface of the interconnect dielectric material. Anitridation process is then performed that converts the metallicresidues into nitrided metallic residues, and forms a nitridedinterconnect dielectric material surface region on a remaining portionof the interconnect dielectric material and a nitrided metal cap surfaceregion on a remaining portion of the metal cap.

In another aspect of the present application, an interconnect structureis provided that has high electromigration resistance, low currentleakage and enhanced reliability. Specifically, the interconnectstructure of the present application includes at least one conductivestructure embedded within an interconnect dielectric material. Theinterconnect dielectric material includes a nitrided interconnectdielectric material surface region located at an exposed surfacethereof. The interconnect structure of the present application furtherincludes a metal cap stack comprising, from bottom to top, a metal capportion and a nitrided metal cap surface region located on an uppersurface of the at least one conductive structure. The interconnectstructure of the present application even further includes nitridedmetallic residues on a surface of the nitrided interconnect dielectricmaterial surface region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial representation (through a cross sectional view)illustrating a structure including a blanket layer of a sacrificialdielectric material located on an exposed upper surface of aninterconnect dielectric material that can be employed in one embodimentof the present application.

FIG. 2 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 1 after forming at least one openingthrough the blanket layer of sacrificial dielectric material and into atleast a portion of the interconnect dielectric material.

FIG. 3 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 2 after formation of a diffusionbarrier liner, and a conductive structure within each opening, andremoving remaining portions of the blanket layer of sacrificialdielectric material.

FIG. 4 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 3 after formation of a metal cap onan exposed surface of the conductive structure and, optionally, onexposed surfaces of the diffusion barrier liner, and the concurrentformation of metallic residues on the exposed surface of theinterconnect dielectric material.

FIG. 5 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 4 after performing a nitridationprocess.

FIG. 6A is a pictorial representation illustrating a partially nitridedmetallic residue that can be formed in one embodiment of the presentapplication.

FIG. 6B is a pictorial representation illustrating a completely nitridedmetallic residue that can be formed in one embodiment of the presentapplication.

FIG. 7 is a pictorial representation (through a cross sectional view)illustrating the structure of FIG. 5 after forming a dielectric cappinglayer on exposed surfaces of the interconnect structure.

DETAILED DESCRIPTION

The present application, which provides an interconnect structure and amethod of forming the same, will now be described in greater detail byreferring to the following discussion and drawings that accompany thepresent application. It is noted that the drawings of the presentapplication are provided for illustrative purposes and, as such, theyare not drawn to scale. In the drawings and the description thatfollows, like elements are referred to by like reference numerals. Forpurposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the components, layers and/orelements as oriented in the drawing figures which accompany the presentapplication.

In the following description, numerous specific details are set forth,such as particular structures, components, materials, dimensions,processing steps and techniques, in order to provide a thoroughunderstanding of the present application. However, it will beappreciated by one of ordinary skill in the art that the presentapplication may be practiced with viable alternative process optionswithout these specific details. In other instances, well-knownstructures or processing steps have not been described in detail inorder to avoid obscuring the various embodiments of the presentapplication.

Referring first to FIG. 1, there is illustrated a structure including ablanket layer of a sacrificial dielectric material 12 located on anexposed upper surface of an interconnect dielectric material 10 that canbe employed in one embodiment of the present application. The term“blanket layer” as used throughout the present application denotes thata material layer is formed entirely on an exposed surface of anunderlying material layer.

Although not shown, the structure shown in FIG. 1 is typically locatedupon a substrate. The substrate may comprise a semiconducting material,an insulating material, a conductive material or any combinationincluding multilayers thereof. When the substrate is comprised of asemiconducting material, any semiconductor such as Si, SiGe, SiGeC, SiC,Ge alloys, GaAs, InAs, InP and other III/V or II/VI compoundsemiconductors may be used. In addition to these listed types ofsemiconducting materials, the present application also contemplatescases in which the semiconductor substrate is a layered semiconductorsuch as, for example, Si/SiGe, Si/SiC, silicon-on-insulators (SOIs) orsilicon germanium-on-insulators (SGOIs).

When the substrate is an insulating material, the insulating materialcan be an organic insulator, an inorganic insulator or a combinationthereof including multilayers. When the substrate is a conductingmaterial, the substrate may include, for example, polySi, an elementalmetal, alloys of elemental metals, a metal silicide, a metal nitride orcombinations thereof including multilayers. When the substrate comprisesa semiconducting material, one or more semiconductor devices such as,for example, complementary metal oxide semiconductor (CMOS) devices canbe fabricated thereon. When the substrate comprises a combination of aninsulating material and a conductive material, the substrate mayrepresent a lower interconnect level of a multilayered interconnectstructure.

The interconnect dielectric material 10 that can be employed in thepresent application may include any interlevel or intralevel dielectricmaterial including inorganic dielectric materials, organic dielectricmaterials, or combinations thereof. The interconnect dielectric material10 may be porous, non-porous or contain regions and/or surfaces that areporous and other regions and/or surfaces that may be non-porous. Someexamples of suitable dielectrics that can be used as the interconnectdielectric material 10 may include, but are not limited to, siliconoxide, silsesquioxanes, C doped oxides (i.e., organosilicates) thatinclude atoms of Si, C, O and H, thermosetting polyarylene ethers, ormultilayers thereof. The term “polyarylene” is used in this applicationto denote aryl moieties or inertly substituted aryl moieties which arelinked together by bonds, fused rings, or inert linking groups such as,for example, oxygen, sulfur, sulfone, sulfoxide, carbonyl and the like.

In some embodiments of the present application, the interconnectdielectric material 10 has a dielectric constant that is about 3.0 orless, with a dielectric constant of about 2.8 or less being even moretypical. All dielectric constants mentioned herein are relative to avacuum, unless otherwise noted. Dielectric materials that havedielectric constants of about 3.0 or less generally have a lowerparasitic cross talk as compared with dielectric materials that have ahigher dielectric constant than 4.0. The thickness of the interconnectdielectric material 10 may vary depending upon the dielectric materialused as well as the exact number of dielectric layers within theinterconnect dielectric material 10. In one embodiment, and by way of anexample, the interconnect dielectric material 10 may have a thicknessfrom 50 nm to 1000 nm. Other thicknesses that are lesser than or greaterthan the aforementioned thickness range may also be employed for theinterconnect dielectric material 10.

The interconnect dielectric material 10 can be formed utilizing adeposition process. Examples of suitable deposition process that can beused in forming the interconnect dielectric material 10 include, but arenot limited to, chemical vapor deposition (CVD), plasma enhancedchemical vapor deposition (PECVD), evaporation, chemical solutiondeposition and spin-on coating.

After forming the interconnect dielectric material 10, the blanket layerof sacrificial dielectric material 12 is formed on an exposed surface ofinterconnect dielectric material 10. The blanket layer of sacrificialdielectric material 12 may comprise an oxide, nitride, oxynitride ormultilayers thereof (e.g., a sacrificial material stack composed of apad oxide and a pad nitride). In some embodiments, the blanket layer ofsacrificial dielectric material 12 may be composed of a semiconductoroxide, a semiconductor nitride and/or a semiconductor oxynitride. In oneexample, the blanket layer of sacrificial dielectric material 12 may becomposed of silicon oxide and/or silicon nitride.

In some embodiments, the blanket layer of sacrificial dielectricmaterial 12 may be formed by a deposition process. Examples ofdeposition process that may be used in forming the blanket layer ofsacrificial dielectric material 12 include, but are not limited to, CVD,PECVD, evaporation, chemical solution deposition, physical vapordeposition (PVD) and atomic layer deposition. In other embodiments, theblanket layer of sacrificial dielectric material 12 can be formed by athermal process such as, for example, a thermal oxidation, a thermalnitridation and/or a thermal oxynitridation process. In yet otherembodiments, the blanket layer of sacrificial dielectric material 12 canbe formed utilizing a combination of deposition and thermal processes.That is, a thermal oxidation process may be used to form a sacrificialoxide material, followed by CVD to form a sacrificial nitride material.

The thickness of the blanket layer of sacrificial dielectric material 12may vary depending on the number of materials within the blanket layerof sacrificial dielectric material 12 itself as well as the techniquethat was used in forming the same. Typically, the blanket layer ofsacrificial dielectric material 12 has a thickness from 10 nm to 80 nm.Other thicknesses that are lesser than or greater than theaforementioned thickness range may also be used for the blanket layer ofsacrificial dielectric material 12.

Referring now to FIG. 2, there is illustrated the structure of FIG. 1after forming at least one opening 14 through the blanket layer ofsacrificial dielectric material 12 and into at least a portion of theinterconnect dielectric material 10. In some embodiments (not shown),the at least one opening 14 can extend entirely through the interconnectdielectric material 10. In other embodiments, and as illustrated in FIG.2, the at least one opening 14 can extend partially through theinterconnect dielectric material 10.

The at least one opening 14 may include a via opening, a line opening, acombined via and line opening, or any combination thereof. In thedrawings, three via openings are shown by way of a non-limiting example.In some embodiments, a single opening can be formed. In otherembodiments, a plurality (i.e., greater than 1) of openings can beformed. In some embodiments of the present application, each of theopenings 14 may extend a same depth into the interconnect dielectricmaterial 10. In other embodiments, a first set of openings may extend toa first depth into the interconnect dielectric material 10, and a secondset of openings may extend to a second depth into the interconnectdielectric material 10, wherein the second depth is different (less thanor greater than) the first depth. Other depth scenarios are alsopossible and thus the present application is not limited to any specificdepth or depths that the openings 14 can extend into the interconnectdielectric material 10.

The at least one opening 14 can be formed by lithography and etching.The lithographic step includes forming a photoresist (organic, inorganicor hybrid) atop the blanket layer of sacrificial dielectric material 12by a deposition process. Examples of deposition processes that can beused in forming the photoresist include, for example, CVD, PECVD andspin-on coating. Following formation of the photoresist, the photoresistcan be exposed to a desired pattern of radiation. In one example, atrench pattern of radiation can be used. In another embodiment, a linepattern of radiation can be used. Next, the exposed photoresist can bedeveloped utilizing a resist development process well known to thoseskilled in the art.

After the development step, an etching step is performed to transfer thepattern from the patterned photoresist into the blanket layer ofsacrificial dielectric material 12 and thereafter into the interconnectdielectric material 10. The patterned photoresist is typically removedfrom the surface of the structure after transferring the pattern intothe blanket layer of sacrificial dielectric material 12 utilizing aconventional resist stripping process such as, for example, ashing. Theremaining sacrificial dielectric material is then used as an etch maskduring the subsequent transferring of the pattern into the interconnectdielectric material 10. The etching step used in forming the at leastone opening 14 may include a dry etching process (including reactive ionetching, ion beam etching, plasma etching or laser ablation), a wetchemical etching process or any combination thereof In one example, areactive ion etching is used to form the at least one opening 14. Insome embodiments and for forming single damascene structures, a singlelithographic and etching sequence is performed. In other embodiments andfor fabricating dual damascene structures, a first lithographic andetching sequence is performed, and then a second lithographic andetching sequence is performed.

Referring now to FIG. 3, there is illustrated the structure of FIG. 2after formation of a diffusion barrier liner 16 and a conductivestructure 18 within each opening 14, and removing remaining portions ofthe blanket layer of sacrificial dielectric material 12 from atop theinterconnect dielectric material 10. Notably, FIG. 3 shows a planarstructure including conductive structures 18 embedded withininterconnect dielectric material 10, wherein diffusion barrier liner 16is located between portions of the interconnect dielectric material 10and portions of each conductive structure 18.

As shown in FIG. 3, the upper surface of each conductive structure 18embedded within the interconnect dielectric material 10 is coplanar withan upper surface of the interconnect dielectric material 10. The uppersurface of each conductive structure 18, and the upper surface of theinterconnect dielectric material 10 are also coplanar with uppersurfaces of the diffusion barrier liner 16. In some embodiments, and asshown in the drawings of the present application, the diffusion barrierliner 16 is U-shaped. The diffusion barrier liner 16 is a contiguouslayer that is present within each opening 14 that is formed within theinterconnect dielectric material 10.

The structure shown in FIG. 3 is provided by first forming a diffusionbarrier material on the exposed surfaces of the remaining portions ofthe blanket layer of sacrificial dielectric material 12 and on exposedsurfaces of the interconnect dielectric material 10 within each opening14. Next, a conductive material is formed on the exposed surfaces of thediffusion barrier material. A planarization process such as, forexample, chemical mechanical polishing and/or grinding can be used toremove portions of the diffusion barrier material, the conductivematerial and remaining portions of the blanket layer of sacrificialdielectric material 12 from the upper surface of the interconnectdielectric material 10. The remaining portions of diffusion barriermaterial can be referred to herein as diffusion barrier liner 16, whilethe remaining portions of the conductive material can be referred toherein as conductive structure 18.

The diffusion barrier material that can be employed in forming thediffusion barrier liner 16 may be composed of Ta, TaN, Ti, TiN, Ru, RuN,RuTa, RuTaN, IrTa, IrTaN, W, WN or any other material that can serve asa barrier to prevent conductive material from diffusing there through.The thickness of the diffusion barrier material used in forming thediffusion barrier liner 16 may vary depending on the deposition processused as well as the material employed. In one embodiment of the presentapplication, the diffusion barrier material that forms the diffusionbarrier liner 16 has a thickness from 4 nm to 40 nm. Other thicknessesthat are lesser than or greater than the aforementioned thickness rangecan also be employed for the diffusion barrier material. The diffusionbarrier material that forms the diffusion barrier liner 16 may be formedby a deposition process. Examples of deposition processes that can beused in forming the diffusion barrier material include, but are notlimited to, CVD, PECVD, PVD, sputtering and plating.

The conductive material used in forming the conductive structure 18includes, for example, polySi, a conductive metal, an alloy comprisingat least two conductive metals, a conductive metal silicide orcombinations thereof In one embodiment of the present application, theconductive material that is used in forming the conductive structure 18is a conductive metal or conductive metal alloy. In some examples, theconductive metal used in forming the conductive structure 18 includesCu, W, Al, or alloys thereof In one particular embodiment of the presentapplication, Cu or a Cu alloy (such as AlCu) is used as the conductivematerial that forms the conductive structure 18.

The conductive material that is used in forming the conductive structure18 can be formed utilizing a deposition process. Deposition processesthat can be used in forming the conductive material include, but are notlimited to, CVD, PECVD, PVD, sputtering, plating, chemical solutiondeposition and electroless plating.

Referring now to FIG. 4, there is illustrated the structure of FIG. 3after formation of a metal cap 20 on an exposed upper surface of eachconductive structure 18 and, optionally, on exposed surfaces of thediffusion barrier liner 16, and the concurrent formation of metallicresidues 22 on the exposed upper surface of the interconnect dielectricmaterial 10.

The term “metallic residues” is used throughout the present applicationto denote fragments of metal material that is used in providing themetal cap 20 which form on surface of the interconnect dielectricmaterial 10 during the formation of metal cap 20. The metallic residues22 are conductive, and if the metallic residues 22 remain on the exposedupper surface of the interconnect dielectric material 10 in the sameform as which they are formed, the resultant interconnect structurecould exhibit current leakage between adjacent metal lines. In somecases, and if the metallic residues 22 remain on the exposed uppersurface of the interconnect dielectric material 10 in the same form aswhich they are formed, the resultant interconnect structure might beunreliable.

In some embodiments, the metal cap 20 is formed only on the exposedsurface of the conductive structure 18. In other embodiments, the metalcap 20 is formed on exposed surfaces of both the conductive structure 18and the diffusion barrier liner 16. In the drawings, the metal cap 20 isformed only atop the upper surface of each conductive structure 18.

The metal cap 20 that can be employed in the present applicationincludes any metal that is more resistant to corrosion or oxidation thanthe underlying conductive structure 18. In one embodiment of the presentapplication, the metal cap 20 includes Ru, Ir, Rh, Mn Pt, Co, W oralloys thereof. In another embodiment, the metal cap 20 may comprise aCo(W,P, B) alloy. In some embodiments, the metal cap 20 may comprise asingle layer of metal. In other embodiments, the metal cap 20 maycomprise a plurality of metal layers. In some cases, Co is selected asthe material for the metal cap 20.

The thickness of the metal cap 20 may vary depending on the type ofmetal used in forming metal cap 20, the deposition technique andconditions used as well as the number of metals used in providing metalcap 20. In one embodiment, the metal cap 20 has a thickness from 1 Å to100 Å, although other thicknesses that are lesser than or greater thanthe aforementioned thickness range can be used.

The metal cap 20 can be formed by a deposition process. Examples ofdeposition processes that can be used in forming the metal cap 20include, but are not limited to, CVD, PECVD, ALD and electrolessdeposition. In some embodiments, the deposition of the metal cap 20 isperformed at a temperature of greater than 200° C. to a temperature of400° C.

In one embodiment of the present application, the metal cap 20 can beformed utilizing a low temperature chemical deposition processincluding, for example, CVD, PECVD, low pressure (i.e., a pressure of 20torr or less) CVD, ALD or electroless deposition. By “low temperature”,it is meant a deposition temperature of from 75° C. up to, andincluding, 200° C. In some embodiments, the low temperature depositionconditions are selected to provide a deposition rate of the metal cap 20onto the conductive structure 18 that is from 0.2 Å/sec to 0.8 Å/sec. Insome embodiments of the present application, the selective deposition ofthe metal cap 20 on to only the conductive structure 18 is enhanced byutilizing a low k dielectric material (i.e., k about 3.0 or less) asinterconnect dielectric material 10 in conjunction with a lowtemperature chemical deposition process as discussed above.

Referring now to FIG. 5, there is illustrated the structure of FIG. 4after performing a nitridation process. The nitridation process can alsobe referred to herein as a post metal cap treatment. The nitridationprocess of the present application nitridizes, at least partially orentirely, the metallic residues 22 that are present on the exposedsurface of the interconnect dielectric material 10. That is, thenitridation process partially coverts or entirely converts the metallicresidues located on the upper surface of the interconnect dielectricmaterial 10 into nitrided metallic residues which are less conductivethan their non-nitrided metallic residue counterparts. The nitridedmetallic residues are labeled as element 22N in FIG. 5. In someembodiments, an upper portion of the diffusion barrier liner 16 may benitrided as well during this step of the present application.

In addition to nitridizing the metallic residues 22, the nitridationprocess of the present application also nitridizes any exposed surfaceof the interconnect dielectric material 10 forming a nitridedinterconnect dielectric material surface region 24 on a remainingportion of the interconnect dielectric material 10, and any exposedsurface of the metal cap forming a nitrided metal cap surface region 26on a remaining portion of the metal cap 20. The remaining portion metalcap 20 can be referred to herein as metal cap portion 20′. Takentogether, the metal cap portion 20′ and the nitrided metal cap surfaceregion 26 can be referred to as a metal cap stack.

In accordance with the preset application, the nitrided interconnectdielectric material surface region 24 has a higher content of nitride(i.e., nitrogen) than the remaining portion of the interconnectdielectric material 10. Likewise, the nitrided metal cap surface region26 has a higher nitride (i.e., nitrogen) content than the remainingportion of the metal cap 20.

The term “nitrided interconnect dielectric material surface region” isused in the present application to denote a portion of the interconnectdielectric material in which nitride exposure was made. The nitridedinterconnect dielectric material surface region includes a nitrideddielectric material that has a higher content of nitride as compared toremaining portions of the interconnect dielectric material 10 which werenot subjected to the nitride exposure.

The term “nitrided metal cap surface region” is used in the presentapplication to denote a portion of the metal cap material in whichnitride exposure was made. The nitrided metal cap surface regionincludes a nitrided metal cap material that has a higher content ofnitride as compared to remaining portions of the metal cap 20 which werenot subjected to the nitride exposure.

In accordance with the present application, an upper surface of thenitrided interconnect dielectric material surface region 24 is coplanarwith an upper surface of each conductive structure 18.

In one embodiment of the present application, the nitridation processcan be performed utilizing a thermal nitridation process. Thermalnitridation includes heating the structure shown in FIG. 4 in thepresence of a nitrogen-containing source. The heating should beperformed such that oxidation of metallic residue is avoided. Theheating may by performed utilizing any energy source including, forexample, a heating element or a lamp. In some embodiments of the presentapplication, the heating can performed at a temperature from 80° C. to400° C. In another embodiment, the heating can be performed at atemperature from 150° C. to 300° C. In some embodiments of the presentapplication, the heating in the presence of a nitrogen-containing sourcecan be performed at a single temperature. In another embodiment, theheating in the presence of a nitrogen-containing source can be performeda various temperatures using various ramp-up rates and/or soak times.

The nitrogen-containing source that can be used during thermalnitridation includes, but is not limited to, N₂, NO, N₂O, NH₃, N₂H₂ andmixtures thereof. Prior to thermal nitridation, the nitrogen-containingsource can be in any form. However, during the thermal nitridationprocess the nitrogen-containing source is in the form of a gas or vapor.In some embodiments, the nitrogen-containing source can be used neat. Inanother embodiment of the present application, the nitrogen-containingsource can be used in conjunction with an inert ambient such as, forexample, He, Ar, Ne and mixtures thereof. In such an embodiment, thenitrogen-containing source and the inert ambient can be admixed prior tobeing used during thermal nitridation. In yet another embodiment, thenitrogen-containing source and the inert gas can be introduced asseparate components into a reactor and then admixed within the reactoritself prior contacting the surface of the structure shown in FIG. 4.When a nitrogen-containing source/inert ambient mixture is employed, andin one embodiment, the concentration of nitrogen-containing sourcewithin the mixture is from 10% to 90%, the remainder up to 100% is thecontent of the inert ambient. In another embodiment, the concentrationof nitrogen-containing source within the mixture is from 40% to 70%, theremainder up to 100% is the content of the inert ambient.

In another embodiment of the present application, the nitridationprocess can be performed utilizing a plasma nitridation process. Plasmanitridation includes introducing a nitrogen-containing plasma to thestructure shown in FIG. 4. The nitrogen-containing plasma can begenerated by introducing a nitrogen-containing source into a reactorthat can generate the nitrogen-containing plasma. In some embodiments ofthe present application, an RF or microwave power source can be used togenerate a nitrogen-containing plasma within a reactor.

The nitrogen-containing source that can be used in providing thenitrogen-containing plasma includes, but is not limited to, N₂, NO, N₂O,NH₃, N₂H₂ and mixtures thereof. In some embodiments, only anitrogen-containing source is used in providing the nitrogen-containingplasma. In other embodiments of the present application, thenitrogen-containing plasma can be generated from a mixture of anitrogen-containing source and an inert ambient such as, for example,He, Ar, Ne and mixtures thereof In such an embodiment, thenitrogen-containing source and the inert ambient can be admixed prior tobeing introduced into a reactor that generates a plasma. In yet anotherembodiment, the nitrogen-containing source and the inert gas can beintroduced as separate components into a reactor that generates a plasmaand then admixed within the reactor itself prior to generating theplasma. When a nitrogen-containing source/inert gas mixture is employed,and in one embodiment, the concentration of nitrogen-containing sourcewithin the mixture is from 10% to 90%, the remainder up to 100% is thecontent of the inert ambient. In another embodiment, the concentrationof nitrogen-containing source within the mixture is from 40% to 70%, theremainder up to 100% is the content of the inert ambient.

Specifically, FIG. 5 illustrates an exemplary interconnect structure ofthe present application. The illustrated interconnect structure of FIG.5 includes at least one conductive structure 18 embedded within aninterconnect dielectric material 10. The interconnect dielectricmaterial 10 includes a nitrided interconnect dielectric material surfaceregion 24 located at an exposed surface thereof. The interconnectstructure of the present application further includes a metal cap stackcomprising, from bottom to top, a metal cap portion 20′ and a nitridednitrided metal cap surface region 26 located on an upper surface of theat least one conductive structure 18. The interconnect structure of thepresent application even further includes nitrided metallic residues 22Nlocated on a surface of the nitrided interconnect dielectric materialsurface region 24.

Depending on the conditions of the nitridation process, the metallicresidues 22 can be partially nitrided, completely nitride, or a firstset can be partially nitrided and a second set can be completelynitrided. Reference is now made to FIGS. 6A and 6B which illustrate someexemplary embodiments of the present application. Notably FIG. 6Aillustrates a partially nitrided metallic residue that can be formed inone embodiment of the present application, while FIG. 6B illustrates acompletely nitrided metallic residue that can be formed in oneembodiment of the present application. In FIG. 6A, the partiallynitrided metallic residue 50 includes a core 50C containing metallicresidue, and shell 505 that contains nitrided metal. That is, thenitrided metallic residues shown in FIG. 6A comprises a nitridedmetallic shell surrounding a non-nitrided metallic core. In FIG. 6B, theentirety of the nitrided metallic residue 52 contains nitrided metal.

Referring now to FIG. 7, there is illustrated the structure of FIG. 5after forming a dielectric capping layer 28 on exposed surfaces of theinterconnect structure. Specifically, and as shown in FIG. 7, thedielectric capping layer has a bottom surface that contacts an exposedsurface of the nitrided interconnect dielectric material surface region24, nitrided metal cap surface region 26, if exposed, a surface of eachnitrided metallic residue 22N, and also the diffusion barrier liner 16.

The dielectric capping layer 28 comprises a dielectric capping materialsuch as, for example, SiC, Si₄NH₃, SiO₂, a carbon doped oxide, anitrogen and hydrogen doped silicon carbide SiC(N,H) or multilayersthereof. The thickness of the dielectric capping layer 28 may varydepending on the technique used to form the same as well as the materialmake-up of the layer. In one embodiment, and by way of n example, thedielectric capping layer 28 has a thickness from 15 nm to 100 nm. Otherthicknesses that are lesser than or greater than the aforementionedthickness range may also be employed for the dielectric capping layer28. The dielectric capping layer 28 can be formed by a depositionprocess. Examples of deposition processes that can be used in formingthe dielectric capping layer 28 include, but are not limited to, CVD,PECVD, evaporation, spin-on coating, chemical solution deposition andPVD.

While the present application has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present application. It is therefore intended that the presentapplication not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

What is claimed is:
 1. An interconnect structure comprising: at leastone conductive structure embedded within an interconnect dielectricmaterial, wherein said interconnect dielectric material includes anitrided interconnect dielectric material surface region located at anexposed surface thereof; a metal cap stack comprising, from bottom totop, a metal cap portion and a nitrided nitrided metal cap surfaceregion located on an upper surface of the at least one conductivestructure; and nitrided metallic residues on a surface of said nitridedinterconnect dielectric material surface region.
 2. The interconnectstructure of claim 1, wherein said at least one conductive structure iscomposed of copper or a copper alloy.
 3. The interconnect structure ofclaim 1, wherein said nitrided metallic residues comprise a nitridedmetallic shell surrounding a non-nitrided metallic core.
 4. Theinterconnect structure of claim 1, wherein said nitrided metallicresidues comprise a same metal as said metal cap stack.
 5. Theinterconnect structure of claim 1, further comprises a U-shapeddiffusion barrier liner positioned between each conductive structure andportions of said interconnect dielectric material.
 6. The interconnectstructure of claim 1, wherein said nitrided interconnect dielectricmaterial surface region has a higher content of nitride as compared tothe interconnect dielectric material.
 7. The interconnect structure ofclaim 1, wherein said nitrided metal cap surface region has a highercontent of nitride as compared to said metal cap portion.
 8. Theinterconnect structure of claim 1, wherein said nitrided interconnectdielectric material surface region has an upper surface that is coplanarwith the upper surface of each conductive structure.
 9. The interconnectstructure of claim 1, wherein said nitrided metallic residues, saidnitrided metal cap surface region and said metal cap portion are eachcomprised of cobalt.